With Cartes du Ciel-SkyChart it is easy to install popular ready-to-use catalogs. You can download and use them for free. Most catalogs aren't larger than some tens of megabytes, these will be helpfull to many dedicated amateurs.
But maybe you want to push things a little further. For example, you want your charts to display stars to a magnitude of 19. Then you need to download the USNO-A2.0 catalog. Before you start downloading, consider its size. Installed, this catalog will consume 6.11 GB. Still interested? See The large catalogs

You also can choose to build your own catalog. As a basis you can choose from thousands of existing catalogs and modify them for usage in Cartes du Ciel-SkyChart. You also can gather information in your own ASCII-file. To use these kinds of catalogs, you need the tool CatGen to adapt them for Cartes du Ciel-SkyChart. Those catalogs demand a little more time before you can use them in Cartes du Ciel-SkyChart. But this is a chapter about the ready-to-use catalogs, so lets continue with that:

To get to the source of those catalogs you go to the download link from the Cartes du Ciel-SkyChart homepage. A SourceForge-page dedicated to Cartes du Ciel-SkyChart will be opened inside the Cartes du Ciel-SkyChart page. Then, to go to the catalogs, click 2-catalogs. Or skip this, and go directly to the catalog download section by a click here.

When you want to install these catalogs for all users, you need to have Administrator (Windows) or root (Linux) rights. If you don't have these, you can choose to install the catalogs somewhere in your computer where you have sufficient rights. (For example, your home directory.)
Download the catalog files that you want, save them (temporary) somewhere on your computer. Use your favorite unzip-program to decompress the files to the installation directory of Cartes du Ciel-SkyChart. With Windows this is typically something like C:\Program Files\Ciel, with Linux ususally this is /usr/share/skychart. But you can choose another path. Remember to configure the path to your catalog with Setup → Catalog.

You can activate or deactivate your catalogs with the dialog boxes from Setup → Catalog. Click the appropriate tab for your specific catalog.

HST-GSC is an acronym for „Hubble Space Telescope Guide Star Catalogue”. The original goal was to keep the HST properly pointed at its target. This catalog contains over 19 million objects brighter then magnitude 16, of which 15 million were identified as stars. This catalog is considered obsolete. Only to be complete, I 'll describe how to retrieve this catalog. I recommend you to use the HST GSC Compact.

This large catalog is available from ftp://adc.gsfc.nasa.gov/pub/adc/superseded/1/1220/GSC/. After you have done everything that is needed to use this catalog, you will discover that this catalog consumes 1.18 GB of space. The .gsc files in this version contain ASCII data.

In the directory of the ftp-server you find directories and 'tarball' files with names like LFFF.tar.gz. (Yes, there is also a file with the name N0730.tar.) To download this catalog, you can choose to do it in a fast way or a slow way.
The fast way: download all tarball files to your computer, including the N0730.tar. To correct this small error, rename N0730.tar to N0730.tar.gz.
Next step is to 'untar' all tarballs with your favorite archive (unzip) program. (With Windows, I use ZipGenius. Every Linux distribution knows how to deal with tarballs.) Usually, the content of the tarball will be written in a directory with the same name as the tarball with omission of the '.tar.gz' part. In this directory you use your favorite archive program again to decompress every file with the .gz extension.

Watch this: After the untar action, pretty often the contents of the tarballs (i.e. N0000.tar.gz) ends up in a directory export\pub\ftp\pub\adc\archives\superseded\1\1220\GSC\LFFFF, and pretty often they don't. Whatever the result, after decompression move all 'LFFFF' directories with their content to one common directory. After that, set Cartes du Ciel-SkyChart to use the common path with the Setup → Catalog → CDC Stars dialog box.

Downloading the tarball is quite fast, the decompression of all the .gz files however isn't. (It's well possible that it will take you a few hours to do them all.) In any case, this is the fast way. The slow way would be to download every single .gz file from every subdirectory of the FTP-server. And then you still need to decompress them..

From the Cartes du Ciel-SkyChart point of view there is not much difference between the HST-GSC original FITS and the HST GSC Compact. Again, it's based on the data of 19 million objects brighter than magnitude 16, of which 15 million are identified as stars. The size of the HST GSC Compact makes all the difference: on your harddisk it only needs 290 MB. This is because the .gsc files in this catalog are in a binary format.
The original Cartes du Ciel-SkyChart version 2.7x allready could work with the version 1.1. Now, this catalog is considered obsolete. The version 1.2 version became its successor (also obsolete now), at this moment we recommend you the HST-ACT version to serve as your HST GSC Compact catalog. You can download this one from

• ftp://cdsarc.u-strasbg.fr/pub/cats/I/255/GSC_ACT/, or from
  
• ftp://adc.astro.umd.edu/pub/adc/archives/catalogs/1/1255/GSC_ACT/.
  

When your only possibility is to use HTTP, you might consider downloading from

• http://cdsarc.u-strasbg.fr/ftp/cats/i/255/GSC_ACT/.
  

From your download source, copy all files to a local directory. If you still have got the older HST GSC compact versions 1.1 en 1.2, you still can use them with Cartes du Ciel-SkyChart.

Last but not least: Activate your catalog with the Setup → Catalog → CDC Stars dialog box.

As I said earlier, this is a large catalog. It contains data of 526,280,881 stars, among the data are the magnitudes in V and B. The limiting magnitude is at 19+. Unfortunatly, this catalog doesn't contain data about the proper motion.
There are some versions of the 'USNO A' catalogs, the most recent is USNO A version 2.0. There is also a smaller subset from the 'USNO A' catalog. This summary is considerable smaller and is called USNO-SA 2.0.
And then there is the USNO B version. Since the arrival of this catalog, the professionals consider USNO A2.0 as obsolete. USNO B contains data of 1 billion objects, complete with data about their proper motions. Unfortunatly, at the moment I don't know of FTP-sources to do a complete download of this catalog. At this moment (2009-01-25), Cartes du Ciel-SkyChart version 3 can't retrieve the data from online catalogs. In future releases, Cartes du Ciel-SkyChart will be able to retrieve the data catalog servers at the Internet. So, for the moment, stick with USNO A 2.0. It will do.

The installed catalog will occupy 6,11 GB on your media. To download the USNO-A2.0 catalog, use your favorite FTP-client like Filezilla to copy everything from

• ftp://ftp.nofs.navy.mil/pub/outgoing/usnoa/ (uncompressed) or from
  
• ftp://adc.astro.umd.edu/pub/adc/archives/catalogs/1/1252/usnoa/ (gz-compressed, use your favorite archive program like ZipGenius).
  

Wherever you retrieve your USNO-A catalog from, make sure that (after eventually decompression) your catalog contains files with a .acc and .cat extensions. Files from ftp://cdsarc.u-strasbg.fr/pub/cats/I/252/USNO_A2 contain files with a .ppm extension. I didn't get these to work with Cartes du Ciel-SkyChart, save yourself from this dissapointment.

Copy files one by one. If you don't do that, you 'll risk that your process will be killed at the server site, simply because your task allocated to much memory. (These files are large, remember?) After downloading, put all the files together in one directory if you didn't do that allready. Worth knowing might be that the FTP-server from ftp.nofs.navy.mil only accepts 'passive' connections. With the modern FTP-clients, that shouldn't be much of a problem. And keep in mind that those servers can be busy, despite their sluggish Internet connection. Be patient.

And again: Activate your catalog with the Setup → Catalog → CDC Stars dialog box